The present invention is directed to an arrangement for significantly increasing the lifetime and recording density of magnetic disk storage devices having concentric data tracks or bands, limit bands and/or landing bands or zones as well as read/write heads located on or extremely closely above the surface of at least one disk independently of the operating state.
Magnetic disk storage devices have proven their suitability for storing large quantities of data in the field of data processing over a long period of practical use. Two basic types are essentially found in use. One type is the removable disk storage device, whose magnetic recording media, the disks, can be removed by hand without problems, whereby the read/write heads with positioning unit and motor disk drive are accommodated in a housing. However, this removability necessitates, among other things, a relatively large distance between the read/write heads and the surface of the disks, with the result that the recording density and recording capacity are limited. For this reason, the rigid disk storage device has established itself more and more, whereby its disks cannot be removed, but its read/write heads can remain in certain zones between the disks irrespective of the operating state. It is thus possible to considerably simplify the mechanical construction, to fully encapsulate the disks, heads and/or motor drive or to integrate these in a housing with air filter. This has in turn resulted in a considerable reduction in the distance between the read/write head and the disk and has increased the recording density. Such a storage device is described, for example, in U.S. Pat. No. 3,849,800. An improved type of this storage device is described, for example, in U.S. Pat. No. 4,034,411. In order to improve the storage capacity by way of a higher recording density, the head distance from the recording medium was further reduced and, in addition, the track density was increased, whereby this was made possible particularly through better design of the flying heads and carriers for the heads. Such embodiments are known, for example, from U.S. Pat. No. 4,961,121 and EU-A1-0308527. These are intended above all to reduce the distance between the head and disk and prevent undesired contact with the disk surface during operation. Contact with the surface of the recording medium during operation leads to total information or data loss and also renders the storage device unusable. The fact that the economic damage caused by this is very great both for manufacturer and user is shown, among other things, by. the article "Oil slick mires IBM drives" in Electron. News Jun. 12, 1989. In addition, these topics and problems were discussed at the "EUROPEAN DATA STORAGE INTERFACE AND TECHNOLOGY CONFERENCE III" on 25th and 26th Sep. 1991, without demonstrating a practicable solution. In this context, reference should be made to the "DISK ARRAY FORUM CONF. BOOK", issued by TECHNOLOGY FORUMS LTD., 15612 Highway 7, Suite 210, Minnetonka, Minn. 55345, USA. Gene E. Milligan of Seagate Technology Inc., in SESSION I, and Tom Glaser, IBM, "Future trends in rigid disk technology and their impact on disk arrays", Sep. 91 in SESSION VIII, discuss the problems of the low flying height of magnetic heads, the use of lubricants and the difficult process involved in contact between the head and disk during reading and recording. However, no publication shows a feasible solution, particularly with respect to avoidance of total failure due to undesired contact between the head and disk. On the contrary, only very complex methods and arrangements are suggested, as are also described in U.S. Pat. No. 4,795,981 and EU-A1-0294761; here, the magnetic head distance from the surface of the data medium is measured during operation, and reference signals are recorded, read and measured in order to prevent the destruction of data and disk and to thus also increase the lifetime of rigid disk storage devices. These methods and arrangements are technically complex and expensive, but do not solve the real problem. A method is also described in U.S. Pat. No. 4,692,832 which is intended to solve the said problem of the short operating time such that the disk storage device is slowly conditioned for continuous operation to a certain extent by running the assembly at low velocity in a dry gas atmosphere, whereby the heads fly over all tracks during a start-up time of between 1-4 minutes. Actual storage operation can commence only after this time has elapsed. Apart from the fact that these measures extend the access times, they also do not solve the real problem of increasing the lifetime by preventing destruction of the disks and/or heads.
The cause of undesired head crashes with resultant total data-loss in rigid disk units and destruction of the latter has not yet been fully clarified, since unambiguous reconstruction of the event is extremely difficult after destruction.
However, if the following observations are combined in order to create physically unambiguous conditions, it then becomes possible to master head crashes on the disk, particularly on the data tracks.
The following observations have been made in tests and studies over the course of many years:
A. "Flown-over" surfaces of exchangeable disks are shiny, "non-flown-over" surfaces are dull. However, at least 16000 running hours (2 years) are necessary before this effect can be observed; this is one of the reasons why this effect has not drawn attention to itself. PA1 B. Collections of dirt can be found on the head after continuous operation on one track. PA1 C. Sticking of the heads on the surface of the disk at standstill depends very greatly on the temperature and air humidity in the head/surface area. The lubricant on the disk surface also has a significant influence here. PA1 D. Undesired and destructive contact between the head and disk, i.e. CRASHES, mainly occurs on track 0 or the landing zone. PA1 1. If the flown-over disk=shiny surface and non-flown-over disk=dull surface, there must be a contamination pressure against the surface of the disk which is influenced by the read/write head and which produces a "flying edge" during operation. PA1 2. This conclusion can be transferred from the exchangeable disk to the rigid disk, although clean room conditions exist here through encapsulation and built-in filters. PA1 3. The "flown-over" surface of the disk is clearly defined in physical terms and the read/write head must encounter optimum, that is to say identical or uniform, gliding conditions.
The following conclusions have been drawn by inclusion of the observations made in A in the overall considerations: